Nocturnal light pollution and underexposure to daytime sunlight: Complementary mechanisms of circadian disruption and related diseases

Abstract

Routine exposure to artificial light at night (ALAN) in work, home, and community settings is linked with increased risk of breast and prostate cancer (BC, PC) in normally sighted women and men, the hypothesized biological rhythm mechanisms being frequent nocturnal melatonin synthesis suppression, circadian time structure (CTS) desynchronization, and sleep/wake cycle disruption with sleep deprivation. ALAN-induced perturbation of the CTS melatonin synchronizer signal is communicated maternally at the very onset of life and after birth via breast or artificial formula feedings. Nighttime use of personal computers, mobile phones, electronic tablets, televisions, and the like--now epidemic in adolescents and adults and highly prevalent in pre-school and school-aged children--is a new source of ALAN. However, ALAN exposure occurs concomitantly with almost complete absence of daytime sunlight, whose blue-violet (446-484 nm λ) spectrum synchronizes the CTS and whose UV-B (290-315 nm λ) spectrum stimulates vitamin D synthesis. Under natural conditions and clear skies, day/night and annual cycles of UV-B irradiation drive corresponding periodicities in vitamin D synthesis and numerous bioprocesses regulated by active metabolites augment and strengthen the biological time structure. Vitamin D insufficiency and deficiency are widespread in children and adults in developed and developing countries as a consequence of inadequate sunlight exposure. Past epidemiologic studies have focused either on exposure to too little daytime UV-B or too much ALAN, respectively, on vitamin D deficiency/insufficiency or melatonin suppression in relation to risk of cancer and other, e.g., psychiatric, hypertensive, cardiac, and vascular, so-called, diseases of civilization. The observed elevated incidence of medical conditions the two are alleged to influence through many complementary bioprocesses of cells, tissues, and organs led us to examine effects of the totality of the artificial light environment in which humans reside today. Never have chronobiologic or epidemiologic investigations comprehensively researched the potentially deleterious consequences of the combination of suppressed vitamin D plus melatonin synthesis due to life in today's man-made artificial light environment, which in our opinion is long overdue.

Circadian disruption: New clinical perspective of disease pathology and basis for chronotherapeutic intervention

“…Acute and chronic ingestion of most β-receptor medications in the late evening or before bedtime can delay the Φ and/or depress the A and/ or mean level of the melatonin circadian rhythm (see Smolensky et al, 2015b). Indiscriminate ingestion of melatonin at the wrong biological time to manage dyssomnias and certain other medical conditions of youngsters (delayed sleep phase syndrome, attention-deficit hyperactivity disorder, autism spectrum disorder, mood and anxiety syndromes and some neurologic conditions) and adults, including jet-lag symptoms of travelers transported rapidly across time zones and employees of rotating day/night work schedules, in an attempt to alleviate CD and associated symptoms may actually enhance CD with the possibility of elevated risk of ill effects over the long term (see review by Smolensky et al, 2015a;Stevens, 2006). Chronic cyclic nocturnal enteral and parenteral nutrition to manage short bowel syndrome, intestinal failure and other alimentary tract conditions so as not to restrict diurnal activities is also associated with CD, with alteration of the Φ of the 24 h rhythms in core body temperature (Nishimura et al, 1992); gastric acid secretion (Bouglé et al, 1985); cortisol, parathyroid and insulin hormones (Goodman et al, 2000;Matuchansky et al, 1985;Saito et al, 1989); blood glucose, cholesterol, free fatty acid and/or triglyceride concentrations (Matuchansky et al, 1985;Saito et al, 1989); and renal function and urinary analytes (BoncompainGérard et al, 2000).…”

“…ALAN is viewed today as a major threat to human health and well-being. Epidemiologic, clinical and laboratory animal investigations reveal evidence of increased risk for a broad array of medical conditions, including obesity; metabolic syndrome; diabetes; hypertension; cardiovascular disease; and breast, prostate, colorectal and other cancers (Arble et al, 2015;Cho et al, 2015;Cuesta et al, 2016;Haus & Smolensky, 2013;Johnston et al, 2016;Maury et al, 2014;Reitz & Martino, 2015;Rybnikova et al, 2016;Schernhammer et al, 2003;Smolensky et al, 2015a;Stevens & Zhu, 2015;Stevens et al, 2014;Uth & Sleigh, 2014;Van Cauter et al, 2008). The hypothesized mechanism is ALAN-induced alteration of the CTS, including the 24 h sleep/wake cycle.…”

Artificial light-at-night – a novel lifestyle risk factor for metabolic disorder and cancer morbidity

“…Generally, the indole hormone rhythm is highly sensitive to every type of circadian disruption, including sleep disorder, jetlag, shift work, and most important ALAN [48,137]. MLT levels, measured as 6-SMT, have been found to be significantly reduced in night shift workers compared with counterpart day workers, and the effect correlates positively with the intensity of ALAN and the number of nights worked [221].…”

“…Furthermore, a different study demonstrated an inverse association between MLT synthesis and the irradiances of narrowband blue LED exposure (peak λ = 469 nm; ½ peak bandwidth = 26 nm), and the impact of this spectrum was evidently larger than that of 4000 K of white florescent at twice the energy of the former [44,47]. Finally, the negative effects of circadian disruption on public health are expected to be exacerbated by the increasing exposure to ALAN of LED illumination emitted from variant sources, including electronic screens used by people of all ages, particularly adolescents [48]. ALAN-induced circadian disruption has been related to several health risks, including overweight, obesity, and cancer [49,50].…”

“…Breast cancer is the most prevalent malignancy among western women and has been increasingly being associated with circadian disruption provoked by shift work, jetlag, sleep deprivation, and ALAN exposures [48,[135][136][137]. ALAN exposure as a prevailing feature of our modern 24/7 (h/days) active society is recognized as the most powerful factor, behind circadian disruption [138-140; Figure 2].…”